1. Field of the Invention
The present invention relates to a color image forming apparatus and an image output method connected to a network.
2. Description of the Related Art
With the recent trend in more and more copying machines going digital, multifunctional machines equipped with a plurality of functions have been put into practical applications, including such applications as using a scanner or printer of a copying machine for transmitting and receiving data through facsimile and printing page image by reconstructing it from PDL (Page Description Language) data available from a computer or the like. Such a multifunctional machine is arranged so as to be able to operate even among a plurality of functions, such as, for example, transmitting PDL-converted image through facsimile, in addition to a single function of a copying function, a facsimile function, a PDL printing function, or the like. In addition, the multifunctional machine may also be configured so as to allow, when connected to an individual apparatus such as a computer or the like over a LAN, the computer or the like to use the functions provided by the multifunction machine.
In such multifunctional machines, a common control program for a printer portion is shared among the copying machine function and the PDL print function or facsimile function or the like. Or, a common control program for a reader is shared among the copying machine function and the facsimile function or a scanner function or the like. This approach allows the capacity required for the control programs for realizing the various functions to be reduced, thus achieving the required functions economically and in a simplified manner.
Further, by providing such a multifunctional machine with a large-capacity hard disk capable of storing image data, it is possible to store and control data representing an image scanned by the scanner, an image reconstructed through PDL, a document received by facsimile, or the like as an image file or a document file in the hard disk.
In a printing unit of a color printer in an image forming apparatus, on the other hand, it is known that variations in output characteristics and unit-to-unit variations as a result of these variations in output characteristics occur, which makes it difficult to achieve an output image of a uniform quality. It is known, for example, that printed images of different tones of color result each time a printing process is carried out even using the same original.
This is attributable to the following fact in a printing unit employing, for example, an electrophotographic method. Specifically, in such an electrophotographic process as laser exposure, formation of an electrostatic latent image on a photoconductive element, development of toner, toner image transfer to a paper medium, or fusing of the toner image onto the paper medium by heat, there occurs a change in an ambient temperature or humidity surrounding the apparatus, or a change in any of component parts of the apparatus with time, which eventually results in the amount of toner fused on the paper medium being varied. It is known that such instability in printing output characteristics is not unique only to the electrophotographic method, but the phenomenon occurs likewise in an ink jet method, a thermal transfer method, and other various methods.
Calibration processing is then carried out. In the calibration processing, an image of a predetermined test gradation pattern is produced, an image density of the pattern produced is measured, and printing characteristics of the printing unit are then corrected based on the results of the measurement of the image density.
An image forming apparatus itself is, however, used for producing a printed output of the test gradation pattern or processing measurement data of the image density of the test gradation pattern, even if an image data is transferred or a print command is issued thereto while the printing unit is being calibrated. This makes it impossible for the printing unit to execute the particular printing function. That is, a computer or the like requests a PDL print function, a facsimile function, or the like to be executed through a network, regardless of whether the calibration process is being carried out or not in the image forming apparatus. This results in a print command being rejected, or a process for generating image forming data, such as rasterization of PDL data, being initiated after the completion of calibration. As a result, printing processing is retarded.
It is therefore a first object of the present invention to provide a color image forming apparatus and an image output method capable of producing a PDL output without interfering with the execution of a calibration process, when the execution of a PDL print function is requested over a network during execution of the calibration process.
It is a second object of the present invention to provide a color image forming apparatus and an image output method capable of producing an output of a facsimile-received document without interfering with the execution of a calibration process, when the execution of a facsimile reception and print function is requested over a network during execution of the calibration process.